1. Field of the Invention
This invention relates to a gas sensor adapted for use with an exhaust gas purification system of an automobile or the like using a three-way catalyst.
2. Description of the Prior Art
A well-known gas sensor is disclosed in U.S. Pat. No. 3,959,765 Specification. This device comprises a sensor element of a transition metal oxide in sintered form, a pair of electrodes embedded in the sensor element, a ceramic member including a pair of small holes for accommodating the pair of electrodes and a pair of large through holes for accommodating a pair of lead pins for taking out the change of the resistance value of the sensor element, and means of electrical conduction made of a conductive glass interposed between the electrodes and the lead pins.
A further study of the gas sensor of the conventional construction shows that it has the problems described below.
(1) In order to uniformly fill the conductive glass in the electrical connection between the lead pins and the electrodes, the lead pins are required to be driven into the conductive glass to press the conductive glass when being melted. This in turn requires a lead pin of large diameter for increasing the pressing area thereof, with the result that the ceramic member large in diameter is required, thus leading to a bulky sensor.
(2) A precious metal such as platinum high in heat resistance and anticorrosiveness is used for the electrode pair. This conventional electrode pair is unnecessarily long and high in cost.